macbates
Well-known member
I’ve been having a problem lately with many of my processed images having stars with red centers, and although I know when this is happening in the processing chain, I can’t figure out why. For the stars in question, if I examine the Canon raw (CR2) files with the readout cursor, the RGB values are 1, 1, and 1, indicating that the star is saturated, and the stars show as white, which is expected with those RGB values.
After running the images through the WBPP script however, those stars have a bright red center, and the readout cursor now shows (typically) RGB values of 1.0, 0.15, and 0.15. With those values I would expect red to be the dominant color, but I don’t understand why the RGB ratio changed. I did some further looking, and it turns out that the stars “change color” after the debayering process. To investigate further, I processed the files by hand instead of using WBPP (bias and dark integration, flat calibration and integration, etc), and right after the debayering process, the output files had stars with red centers.
This is apparently due to the stars being saturated, so for one last test I fed the same raw files through Deep Sky Stacker. The resulting stacked and registered output file from DSS showed the stars as white, with no red centers. Loading the DSS output file into PI, I checked the same star with the readout tool, and got RGB readings of 0.706, 0.865, and 0.782. A bit on the greenish blue side, but that might be explained due to the Astronomik CLS filter in the camera.
So, from the above (condensed from many hours of experimenting) it appears that the Debayering process in PI is turning any and all saturated stars into ones with red centers. More accurately, all pixels with an RBG value of 1,1, 1 are now turned into pixels with red being the dominant color.
I’m stumped as to where to go from here and/or how to fix this problem. As far as I can tell I have all PI settings correct, including using pure raw. Any ideas as to what the problem might be or what I should try next?
Thanks in advance for any ideas, suggestions, or help,
- Ken
After running the images through the WBPP script however, those stars have a bright red center, and the readout cursor now shows (typically) RGB values of 1.0, 0.15, and 0.15. With those values I would expect red to be the dominant color, but I don’t understand why the RGB ratio changed. I did some further looking, and it turns out that the stars “change color” after the debayering process. To investigate further, I processed the files by hand instead of using WBPP (bias and dark integration, flat calibration and integration, etc), and right after the debayering process, the output files had stars with red centers.
This is apparently due to the stars being saturated, so for one last test I fed the same raw files through Deep Sky Stacker. The resulting stacked and registered output file from DSS showed the stars as white, with no red centers. Loading the DSS output file into PI, I checked the same star with the readout tool, and got RGB readings of 0.706, 0.865, and 0.782. A bit on the greenish blue side, but that might be explained due to the Astronomik CLS filter in the camera.
So, from the above (condensed from many hours of experimenting) it appears that the Debayering process in PI is turning any and all saturated stars into ones with red centers. More accurately, all pixels with an RBG value of 1,1, 1 are now turned into pixels with red being the dominant color.
I’m stumped as to where to go from here and/or how to fix this problem. As far as I can tell I have all PI settings correct, including using pure raw. Any ideas as to what the problem might be or what I should try next?
Thanks in advance for any ideas, suggestions, or help,
- Ken